IGR J17480-2446: a new class of accreting binaries?

TL;DR

This paper proposes a new class of long-period, low magnetic field pulsars in low-mass X-ray binaries, explaining their origin through magnetothermal evolution and accretion history, exemplified by IGR J17480-2446.

Contribution

It introduces a theoretical framework for the formation of long-period, low magnetic field pulsars, expanding the standard evolutionary scenario of LMXBs.

Findings

Long-period, low magnetic field pulsars can form through specific accretion histories.

IGR J17480-2446 is identified as belonging to this new pulsar class.

Abstract

The recent discovery of long-period, low magnetic field pulsars in low-mass X-ray binaries (LMXBs) represents a challenge for the standard evolutionary scenario. These pulsars have a magnetic field strength comparable to that of millisecond pulsars ($\sim 10^8 - 10^9$ G), but their period is at least an order of magnitude longer. We discuss the origin of this new class of pulsars within the standard picture of LMXBs formation and apply our results to the case of IGR J17480-2446. The magnetothermal evolution of the binary system is studied numerically by taking into account the effect of different accretion rates during the Roche-lobe overflow in the framework of the minimal cooling scenario. We show that, in addition to standard millisecond pulsars, long-period low magnetic field pulsars should also be expected as a possible outcome of the binary evolution, depending on the strength of the accretion rate during the Roche-lobe overflow. In particular, we argue that IGR J17480-2446 belongs to this new class of objects.